The invention relates to a pilot control valve, particularly an electropneumatic control valve for a pneumatic braking system of a vehicle, having a divided valve housing, in which at least one axially adjustable control piston is arranged for actuating a valve seat arrangement. The valve seat arrangement switches the compressed air flow between external connections, in which case the control piston can be acted upon by way of at least one electromagnetic pilot valve for the axial adjustment. The pilot valve is housed in a pilot valve housing part connected with the relay valve housing part. In particular, the present invention relates to a special further development of a valve-internal pressure compensation channel.
A pilot control valve of the above-mentioned type is used particularly within a pneumatic braking system of a vehicle, which valve, especially in this case, is constructed as an electropneumatic control valve. The control valve has the object of adjusting a brake pressure corresponding to the desired braking effect. For this purpose, a brake line originating from the control valve is usually connected with a brake cylinder arranged directly at the vehicle wheel. The brake cylinder generates the braking power required for braking the vehicle wheel by means of a disk or drum brake connected thereto. The defining of the desired pressure value for the electropneumatic control valve takes place mainly electrically. In addition, for reasons of safety, usually a parallel pneumatic control is provided, which parallel control is used in the event of a failure of the electric control.
Such an electropneumatic control valve is known from German Patent Document DE 196 05 562 A1. The control valve has a large-surface control piston which is axially accommodated inside a cylindrical hollow space of the valve housing. In this case, the control piston separates the hollow space into a control chamber as well as a working chamber. On the part of the working chamber, a coaxial hollow journal is constructed on the control piston, which hollow journal is used for actuating an adjacent valve seat arrangement. By means of an axial adjustment of a spring-tensioned valve tube, the valve seat arrangement switches the compressed air flow between an external brake line connection, a supply pressure connection as well as a bleeding connection.
On the part of the control chamber, the control piston can be acted upon by a control pressure which is generated by means of the pilot valve arrangement. Here, the pilot valve arrangement consists of two electromagnetic pilot valves which, as a result of a coordinated energizing of the integrated electric coils cause an increase, holding or decrease of the control pressure within the control chamber. A force resulting from the brake pressure is applied to the opposite side of the control piston.
The valve housing may be divided into two main components, in which case, essentially the valve seat arrangement with the external connections is provided in a bottom relay valve housing part, and the pilot valves are accommodated in a top pilot valve housing part. The hollow spaces inside the valve housing are partly used as pressure chambers for exercising the valve function; however, pressureless valve-internal hollow spaces are partly also provided, for example, for housing the electronic unit for controlling the pilot valves. In this case, it is necessary that the electronic unit is free of excess pressure influences or vacuum influences.
For this purpose, it is generally known to provide a corresponding pressure compensation channel which establishes a connection between the valve-internal hollow space and the atmosphere. Normally, a control valve for a pneumatic braking system of a vehicle or comparable valves are mounted in a manner unprotected from external environmental influences on the vehicle or the like. So that no external environmental influences, such as rain water, can reach the valve-internal hollow space through the pressure compensation channel, it has been attempted to let the outlet opening of the pressure compensation channel exit from the valve housing at a protected point. However, it was found that this solution does not reliably ensure the desired tightness or protection effect. Thus, for example, when the valve is cleaned by means of a steam jet, cleaning water may enter the interior of the valve.
In order to solve this problem, it has also been attempted to extend the bleeding channel from the hollow space directly to the bleeding connection, which is normally provided with an additional muffler which offers the desired protection. An additional protection against the penetration by external environmental influences is achieved in the state of the art in that a pressure compensation element is placed in the pressure compensation channel. The pressure compensation element permits an air exchange on both sides through a porous microstructure and simultaneously prevents water from entering in the direction of the hollow space.
This known measure also has unsatisfactory results. The pressure compensation channel leading out in the area of the bleeding connection of the valve, as a result of a reaction of the pressure existing here when the valve is bled, leads to an undesirable pressure excess in the electronic space.
It is therefore an object of the present invention to further improve the above-described pilot control valve such that an effective pressure compensation of a valve-internal hollow space is achieved using simple devices and measures.
This and other objects are achieved by providing a pilot control valve, particularly an electropneumatic control valve for a pneumatic braking system of a vehicle, having a divided valve housing, in which at least one axially adjustable control piston is arranged for actuating a valve seat arrangement, which switches the compressed air flow between external connections. The control piston is being capable of being acted upon by way of at least one electromagnetic pilot valve for axial adjustment, which pilot valve is housed in a pilot valve housing part connected with the relay valve housing part. For bleeding a pressureless valve-internal hollow space, a multiple-bend pressure compensation channel is provided, which is formed in the area of the wall of the control chamber in the valve housing. The outlet opening of the compensation channel extending to the outside is arranged behind a spaced covering hood on the valve housing in a manner protected from splashing water. The channel section of the compensation channel close to the hollow space is provided with an exchangeable pressure compensation element.
The invention technically provides that, for bleeding a pressureless valve-internal hollow space, a multiple-bend pressure compensation channel is formed in the area of the wall of the control chamber in the valve housing. Its outlet opening extending to the outside is arranged behind a spaced covering hood on the valve housing in a manner protected from splashing water and its channel section close to the hollow space is provided with an exchangeable pressure compensation element.
The advantage of this special channel construction is, in particular, that pressure compensation now takes place in a housing area of the valve to the outside which, as a result of the covering hood provided for a different purpose, is arranged in an already relatively protected manner from penetration by splashing water and dirt. The developed embodiment of the pressure compensation channel represents another effective protective measure. A pressure compensation element is inserted only in the area of the pressure compensation channel close to the hollow space, which pressure compensation element is easily mountable or exchangeable because of the external accessibility. For the connection of an electronic unit housed inside the hollow space constructed as an electronic space, a corresponding electric connector arrangement may be arranged on the valve housing, which connector arrangement is provided with the covering hood for protecting against external environmental influences. The covering hood is preferably simultaneously used for the protection of the outlet opening of the pressure compensation channel which, to this extent, is also placed behind this covering hood. The specific sequence of these measures provides a protected and effective pressure compensation.
The valve housing of the pilot control valve is normally produced by casting. The valve-internal pressure compensation channel can advantageously be formed in the valve housing directly during the casting. Furthermore, it is also contemplated to form the pressure compensation channel after the production of the valve housing by drilling or the like.
When the pilot control valve is constructed as an electropneumatic control valve for a compressed-air system of a vehicle, the valve housing is preferably constructed of a separate relay valve housing part and also a separate pilot control valve housing part correspondingly constructed in a common connection plane. In this case, the two housing parts are fastened to one another in a pressure-sealed and releasable mannerxe2x80x94for example, by means of screwingxe2x80x94by way of an essentially ring-shaped sealing element which encloses the interior control chamber. The valve housing divided in this manner permits a simple mounting of the interior valve components.
In the case of the valve housing constructed in this manner, the pressure compensation channel may be arranged on the outlet side in the case of the relay valve housing part and may be continued by way of a corresponding opening in the sealing element inside the pilot valve housing part toward the electronic space. By means of this course of the channel, the above-described desired position of the outlet opening of the pressure compensation channel is achieved, in which case the constructional marginal conditions existing as a result of the divided construction of the valve housing are taken into account.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings.